1. Field of the Invention
The present invention generally relates to the field of implantable heart stimulation devices, such as pacemakers, implantable cardioverter-defibrillators (ICD), and similar cardiac stimulation devices that also are capable of monitoring and detecting electrical activities and events within the heart. More specifically, the present invention relates to a device for monitoring cardiac synchrony in a human heart, a system including such a device, an implantable cardiac stimulator comprising such a system, and a method of determining cardiac synchrony in a human heart.
2. Description of the Prior Art
Implantable heart stimulators that provide stimulation pulses to selected locations in the heart, e.g. selected chambers, have been developed for the treatment of cardiac diseases and dysfunctions. Heart stimulators have also been developed that affect the manner and degree to which the heart chambers contract during a cardiac cycle in order to promote the efficient pumping of blood. The heart will pump more effectively when a coordinated contraction of both atria and both ventricles can be provided.
In a healthy heart, the coordinated contraction is provided through conduction pathways in both the atria and the ventricles that enable a very rapid conduction of electrical signals to contractile tissue throughout the myocardium to effectuate the atrial and ventricular contractions. If these conduction pathways do not function properly, a slight or severe delay in the propagation of electrical pulses may arise, causing asynchronous contraction of the ventricles which would greatly diminish the pumping efficiency of the heart. Patients who exhibit pathology of these conduction pathways, such as patients with bundle branch blocks, etc., can thus suffer compromised pumping performance.
Various prior art procedures have been developed for addressing these and other disorders. For instance, cardiac resynchronization therapy (CRT) can be used for effectuating synchronous atrial and/or ventricular contractions. Furthermore, cardiac stimulators may be provided that deliver stimulation pulses at several locations in the heart simultaneously, such as biventricular stimulators. The stimulation pulses could also be delivered to different locations with a selected delay in an attempt to optimize the hemodynamic performance, e.g. maximize cardiac output, in relation to the specific cardiac dysfunction present at the time of implant.
However, even though ventricular and atrial synchrony may be present at the time of implant, possibly supported by suitable cardiac stimulation therapy, this may not necessarily be the case at a later stage. For instance, during progression of cardiac therapy after implantation of a cardiac stimulator, the cardiac tissue may adapt itself to the new conditions. Then, the function of hibernating myocardial tissue may be at least partially restored, and the overall cardiac function may become different from that at the time of implant.
In other words, ventricular and atrial synchrony from the time of implant may turn into asynchrony at a later stage, possibly supported or induced by stimulation therapy, as a result of a local improvement in the local function of myocardial tissue. For instance, the functions of myocardial portions or regions that at the time of implant were affected by slow conduction or post-systolic contractions (PSC), could at a later stage have improved their behavior such that there is no longer any slow conduction or PSC, or the PSC patterns have changed. Thus, even though there is an improvement in the behavior of myocardial tissue through the remodulation or recovery of the heart during progression of cardiac therapy, there may be an impairment in the overall function of the heart since the pacing therapy is not adapted to the new situation. During follow-up, a physician may alter the delay settings in adaptation to altered cardiac status. However, a need still exists for monitoring changes in ventricular and/or atrial synchrony in the heart of a patient.